The invention relates generally to key switch assemblies and, more specifically, to key switches in keyboards for compact or portable use.
Key switches for various types of keyboards, such as computer keyboards, are well known in the art. Typically, these keyboards include a scissor linkage that supports a key cap. When the key cap is depressed, a dome under the key cap causes a switch to be closed. The scissor linkage supports the key cap and allows it to move up and down during use. The dome may serve as a spring and also serve to provide the electrical contact between two conductive traces that are situated below the key cap.
Key switches may include a flex membrane. The flex membrane typically consists of multiple layers. A base layer and a top layer may include one or more electrical contact points that contact each other to complete an electrical circuit, thereby registering a key stroke. A spacer layer separates the base layer and the top layer in an open, or extended key position. The scissor linkage may be secured to the flex membrane with a key cap resting on top of the linkage.
While conventional scissor linkages for keys and key switches are useful for desktop keyboards, they do tend to require a large vertical space. Thus, such key switches are not conducive for use in folding keyboards, which are designed to fold into small spaces when not in use. Co-pending U.S. patent application Ser. No. 09/540,669, filed Mar. 31, 2000, entitled xe2x80x9cFoldable Keyboard,xe2x80x9d describes an example of such a foldable keyboard. This application is hereby incorporated herein by reference. Folding keyboards often require thinner key switches than are used in desktop or laptop computers. The thinner the key switch, the thinner the final folded keyboard assembly can be made.
One problem of membrane switches is that the layers deform with use. This problem is especially prevalent in small, folding keyboards. Folding keyboards often require very thin key switches compared to desktop or laptop computer keyboards. Key switches designed for use in foldable or collapsible keyboards have a tendency over time to be deformed into a shape that is caused by being depressed over long periods of time. When folded, the key switches may have a tendency to remain in the closed position. Because of the thin key switches, the membranes deform easily. Over time, the key switch may deform to a closed position, even when the keyboard is unfolded. The keys may become permanently shorted rendering the keyboard inoperable.
A spring coupled to a multi-layered flex membrane is described. In one embodiment, the spring may be a layer coupled to the top layer of a key switch membrane. In another embodiment, the spring may be coupled to the key switch between a top layer and a spacer layer. The spring or spring layer may increase the resiliency of the key switch membrane to prevent the flex membrane from deforming.